MATLAB: Vecotrizing a for loop

vectorization

I have been trying to write more efficient piece of code and one obvious aspect of doing that is vectorization.I know the basic stuff about that but here's where I can't figure out. So, I have a cell array "dataCell" in which each cell contains a single vector. The length of the vector varies across the cells. Now, I wish to put all the vectors in a single vector named "dataRow" and to make use of vectorisation, I have two another vectors "startIndex" and "numberOfElements" that give the first and the last index for each vector in dataCell that it should occupy in the vector "dataRow". Here is the for loop version of what I wish to do,

for i=1:length(dataCell)
  dataRow(startIndex(i)+1:startIndex(i)+numberOfElements(i))=dataCell{i}
end

Can anyone suggest anything? Thanks!

Best Answer

dataRow = [ dataCell{:} ]

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MATLAB: New values not saving in the matrix after each iteration

You are overwriting the result every iteration, instead of adding it to an existing vector. You could dynamically grow these vectors, but it is better to skip the loop and use logical indexing to directly create the intended vectors. Also, doing a crash course on Matlab can be really useful in getting to know the language.

dat = readtable('170412E1AM1T0.txt');
dat = dat(:, [1 5]);
dat = dat.Variables;
a = dat(8.5 < dat(:,1) &  8.7 > dat(:,1),2);
b = dat(12.5 < dat(:,1) &  12.6 > dat(:,1),2);
c = dat(13.2 < dat(:,1) &  13.4 > dat(:,1),2);
d = dat(14.5 < dat(:,1) &  14.6 > dat(:,1),2);

For your reference, this is the code if you would dynamically grow the vectors:

dat = readtable('170412E1AM1T0.txt');
dat = dat(:, [1 5]);
dat = dat.Variables;
a=[];b=[];c=[];d=[];
for i = 1:length(dat)
    if  8.5 < dat(i,1) &&  8.7 > dat(i,1)
        a = [a;dat(i,2)];
    elseif 12.5 < dat(i,1) &&  12.6 > dat(i,1)
        b = [b;dat(i,2)];
    elseif 13.2 < dat(i,1) &&  13.4 > dat(i,1)
        c = [c;dat(i,2)];
    elseif 14.5 < dat(i,1) &&  14.6 > dat(i,1)
        d = [d;dat(i,2)];
    end
end

Best Answer

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